This VLSI ISO-CMOS device is designed for switching PCM-encoded voice or data, under microprocessor control, in a modern digital exchange, PBX or Central Office. It provides simultaneous connections for up to 256 64 kbps channels. Each of the eight serial inputs and outputs consist of 32 64 kbps channels multiplexed to form a 2048 kbps ST-BUS stream. In addition, the MT8980 provides microprocessor read and write access to individual ST-BUS channels.